By the time the selling ended, the Dow Jones Industrial Average had fallen 166.13 points, closing at 11,823.70, the first triple-digit decline of the year.

The selloff was at least a short-term reversal of a bullish rise that pushed the Dow over the 12,000 level twice this week during interday trading. Although it never closed over 12,000, it reached its highest level since June of 2008.

The event in this case was the Egyptian government’s decision to shut down the Internet and social media connections in the country. As soon as that happened, the price of oil began to rise, ultimately closing the day up $3.68 per barrel, at $89.32 a barrel on the New York Mercantile Exchange, a futures market.

According to an investment memo by Canaccord Genuity, a brokerage house, 1.8 million barrels of oil per day were transported through the Suez Canal in 2009.

“A closure of the canal would result in an extra 6,000 miles of travel for any oil being transported out of the region, an additional cost which could drive up oil prices,” said the brokerage firm.

However, some investors were worried more about the instability spreading beyond Egypt and Tunisia.

“As everyone can see by the following the news flow, this is not confined to a single country,” writes David Kotok, president of Cumberland Advisors, based in Vineland, N.J., in an analysis. “Therefore a contagion risk exists.”

The greatest concern is over Saudi Arabia, which produces 10 million barrels of oil per day. So far, there are no indications of unrest in the country.

Mr. Kotok says as a result of this new risk his firm has sold some stocks and moved more of its money into cash, its first such move since 2009. “We do not know how long we will stay positioned with a cash reserve,” he says. “For now, we going into the weekend with the highest cash reserve since the 2008, post-Lehman-AIG period.”

Dickson says the bullish psychology of the market may have been tempered somewhat by disappointing earnings from Amazon and Microsoft. “Even though Microsoft beat estimates on both the top line and bottom line basis, there was some feeling that the profit margins should have been wider,” he says.

On Friday, the market also considered the government’s report on the fourth quarter gross domestic product to be positive. It showed the economy grew at a 3.2 percent annual rate compared to a 2.6 percent rate in the third quarter. Consumer spending grew at a 4.4 percent annual rate, better than expected. The major drag on the economy was government spending, which shrank, and a slowdown in the rate of growth of inventory accumulation.

Despite the economic news, Dickson says it would not be surprising to see the market retrench in the days ahead. “We may see the decline extend by 3 or 4 percent, which would take it back to a more normal rise if that happens,” he says. “What is happening in Egypt is one of those things where you will just have to see what happens in other countries.”